The present invention relates to a composition for use in a thermally sensitive coating, and a thermally sensitive recording material which utilizes the composition.
A thermally sensitive recording material is a recording material which comprises a base or support layer with a thermally sensitive layer on the base which is capable of forming color upon the application of heat. Thermally sensitive material has been used as a recording paper in a wide variety of environments such as facsimiles and other types of modern recorders and printers.
Recently, with the advent of thermal recording technology which allows for high speed recording, for example, through the use of thermal-recording heads having good heat response characteristics, attempts have been made to provide a "high speed" developer which produces highly dense and stable color pictures for use with the high speed recorders. However, as discussed in U.S. Pat. No. 4,399,188, the low color forming temperatures required (70 to 120 C.) for the high speed recorders has prevented the use of traditional developers, such as bisphenol A, which has a melting point of 156.degree. to 158.degree. C. Therefore, the art has turned to lower melting point developers in an effort to solve this problem. But the use of low melting point developers has introduced their own set of problems with regard to sublimation and stability of the produced image.
In addition to the ability to provide an image with the desired color fastness and density within a high speed recording environment, the recording material must also provide resistance to plasticizers, oil, water, and organic solvents.
Attempted solutions for the above problems have lead to the use of additives and fillers within the thermal sensitive layer. For example, U.S. Pat. No. 4,590,499, to Fujimura et al. relates to a thermal sensitive paper in which the thermal sensitive layer can include a stabilizer, a filler, a sensitizer, a wax resistance additive, a water resistance additive, and surface lubricants.
The use of such large amounts of additives, however, introduces other problems. For example, the presence of waxes and lubricants in their normally used concentration makes the final product slippery to the touch. This gives the perception to the consumer that the thermally sensitive material is not of the same quality as regular bond paper.
Furthermore, the use of fillers which possess high oil absorbance values, subject the print head to undesirable abrasion and possible contamination from partially melted components of the thermal sensitive coating.
In addition, the use of other abrasive fillers such as TiO.sub.2, fumed silica, or calcined clay, which provide the finished product with whiteness, also cause undesirable abrasion of the print head.
Besides the problems associated with the fillers, the use of waxes and lubricants within the coating material requires a complex system for producing the coating because the waxes and lubricants are generally individually prepared within their own individual dispersions and each of the dispersions are then mixed together with the dispersion containing the developer. Such a system is undesirable both in terms of complexity and cost.
Accordingly, it is an object of the present invention to eliminate the need for large quantities of fillers, lubricants and waxes for thermally sensitive coatings.
Further, it is an object of the present invention to provide a simplified process for providing a thermally sensitive coating for high speed recorders utilizing high melting point developers.
These and further objects will become apparent from the specification and claims that follow.